Molecular Dissection of Norovirus Replication and Pathogenesis to Develop Therapeutics Project Summary Noroviruses are the most common cause of gastroenteritis in the United States, and they cause a significant economic and health burden to the population. Critical barriers to controlling human Norovirus infection include the inability to cultivate them in vitro and the lack of specific therapies available to prevent or treat human Norovirus infections. The focus of this program project is to build upon previous basic science and translational findings and discoveries to allow continued progress in our understanding of the biology and pathogenesis of these viruses so that improved control strategies can be developed. We will pursue these activities in three separate projects. In Project 1 we perform studies designed to provide us with a fundamental molecular understanding of the human immune response to Norovirus infection and that influences viral pathogenesis and strain emergence. In addition, we will perform studies to develop treatment and prevention strategies that can be applied to at risk populations. In Project 2 we will determine the basis of restriction to replication in human cells with the overall goal of developing in vitro cultivation methods. We will also evaluate molecular mechanisms by which Norovirus protein expression regulates cellular innate responses and whether these cellular responses regulate viral replication and spread. In Project 3 we will determine the structural basis for novel functions of key proteins that regulate viral replication and virus-host interactions. These projects will be supported by three cores. Core A (Administrative Core) will provide centralized administrative and fiscal management support and will coordinate programmatic activities. Core B (the Microscopy and Flow Cytometry Core) will provide expertise and services to each project related to electron microscopy, fluorescent microscopy and flow cytometry. Core C (the Protein and Small Molecule Chemistry Core) will provide all projects with access to purified proteins and virus-like particles as well as facilitatng site-directed mutagenesis activities needed. In addition, the Core will synthesize small molecules to be used for protease inhibition studies in each project. The program project brings together a highly collaborative group of investigators with diverse skills and talents. As in the previous funding period, the interactions among each project and each of the cores will be extensive such that the activities of each project will be enhanced considerably over what could be accomplished if the projects were pursued independently.